Question Bank • QB_SUB_IDE_0243 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Centrifugal Pumps: Performance Curves & Affinity Laws

Subtopic: Affinity law discharge scaling with speed

Question Statement:

A centrifugal irrigation pump delivers $40.0\text{ L/s}$ against a total head of $20.0\text{ m}$ at a speed of $1450\text{ rpm}$. If the pump speed is increased to $1740\text{ rpm}$ ($1.2 \times 1450$), the new discharge by pump affinity laws (in L/s) is:

Answer Key:

48.0

Step-by-Step Solution & Explanation

Pump affinity law for discharge: $\frac{Q_2}{Q_1} = \frac{N_2}{N_1} \implies Q_2 = 40.0 \times \left(\frac{1740}{1450}\right) = 40.0 \times 1.20 = 48.0\text{ L/s}$
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